Darwin's evidence for evolution: Biogeographic distributions

$(i)$ Environment cannot account for either similarity for dissimilarity, since similar environments can harbor entirely different species groups

$(ii)$ Affinity (similarity) of groups on the same continent (or sea) is closer than between continents (or sea)

$(iii)$ Geographical barriers usually divide these different groups, and there is a correlation between degree of difference and rate of migration of ability to disperse across the barriers